From the author's README on Thunderstore

Baldi's Basics in Education and Learning

Adds Baldi from Baldi's Basics in Education and Learning as a full-body costume for skate.

How to Equip

Open Apparel - Costumes and select Baldi.

Credits

3D model sourced from Baldi on Sketchfab.

Disclaimer

This costume was created separately from the Baldi costume in Unkn0wn's Costume Pack. It was independently ported and rigged by me and does not use the exact Baldi costume from that pack.

Install Baldi

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for Baldi and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.